Delay circuit



April 29, 1947. D. D. GRIEG 2,419,546

'DELAY CIRCUIT Filed March 20, 1942v 00A/ALD 0 639/56 BY MAM Patented Apr. 29, 1947 DELAY CIRCUIT Donald D. Grieg, New York, N. Y., assignor to Federal Telephone Aand Radio Corporation, a

corporation of Delaware Application March 20, 1942, Serial No. 435,498

This invention relates to impulse energy-operated devices and more particularly to an arrangement for producing substantially xedY delay for all applied impulses. The invention is contemplated to have particular utility in impulse-en ergy-operated systems as are employed for the radio location of aircraft and other mobile bodies where xed or adjustably controllable delays may be desirable, and in synchronous transmission of impulse-modulated carrier energy'fr'om two or more mobile units. Suitable radio locator systems which may advantageously employ teachings of this invention have been disclosedin the ccpending applications of H. Busignies Serial Nos. 382,391 and 417,151, led March 8, 1941 and October 30, 1941 respectively, and that of E. Labin Serial No. 383,108, led March 13, 1941.

It is an object of the invention to provide improved means for effectively delaying a series of impulses, recurring uniformly periodically or in amore or less random manner, a predetermined ,amount for each impulse thereof.

Another object is to provide such a device which may yield delayed impulses of sharply-.defined form. v

A further object is to provide an impulse delay network with relatively flexible means for adjusting the effective vdelay thereof.l

Other objects and further features ofnovelty and invention will hereinafter be pointed out or will become apparent to those skilled in the artfrom a reading of the following specication in conjunction with the drawings included herewith. In said drawingsu Fig. 1 is a schematic block diagram of various elements constituting a. preferred form of the invention;

l Fig. 2 is a more detailed circuit diagram of the embodiment shown in Fig. 1;

Fig. 3 is an alternate formyof a portion of the circuit shown in Fig. 2; yand v Fig. 4 is a series of graphical representations of various voltage conditions present in the circuits of the above mentioned figuresall curves being plotted as functions of the same time scale and beginning at the same reference origin.

11 Claims. (Cl. 178-474) y 2 copending application of E.` Labin, Serial vNo.V 386,282, filed April 1, 1941, and U. S. Patent 2,272,070 to Alec Reeves.

In the preferred form of the invention shownv herein, such delay is eliected by the use of applied f impulses to trigger a saw-tooth converter l so Broadly speaking, the invention contemplates effectively delaying each impulse of an applied series ofrecurrent impulses a controlled and, if desired, uniform amount. A particular type of irregular impulse series as contemplated by me for suitable use in this connection is that produced by time-modulation methods. Appropriate apparatus and methods for effecting such modulation have been disclosed, for example, in the that for each applied impulse a newvsaw-tooth wave is commenced. For reasons that will later become apparent, the voltage at which this saw-v tooth Wave commences is preferably thev same.

` The eiective delay is obtained by employing a clipping device I I to clip off the saw-tooth waves at a desired level, whereby the time interval between the start of a saw-tooth Wave and the instant of its being clipped may be the same for all applied impulses, Aeven though these impulses; be irregular in their recurrence. By differenti-v ating the output of clipper II in an appropriate network I2, it is possible to generate a series of impulses corresponding in their pattern of recur--v rence tothe series of applied impulses, said series` being characterized by the desired delay for each impulse thereof. Since the arrangement shown produces additional undesired -impulses of opposite polarity from the delayed impulses, these may thereafter be removed by such known means a a clipper I3.

Considering a preferred form of the invention in more specific detail, reference is made to Fig 2. In this figure, the series of impulses which it is desired to delay is applied through a coupling network I4, I5 to the control grid of an amplifier tube T1 and depending upon Whether or'not it is desirable to have positive or negative impulse voltages applied to the saw-tooth converter circuit, a switching device I6 is provided in the output of tube T1 so that output may be taken either from the anode or cathode circuit for this purpose.A As shown, switch I 6 is set to select impulses from the cathode circuit of tube T1. These impulses will thus be of the same polarity as those applied,` as will be clear. lSaw-tooth converter I0, as seen in Fig. 2, comprises a simple triode T2 having a time-constant output circuit including a resistor I'I shunted to ground by a condenser voltage-dividing arrangement I8, I9. The high voltage B supply to which. resistor II is connected, permits the normal application of a relatively high potential across condensers I8 and I9, that is, in the absence of conductivity of tube T2 (which is preferably normally biased below cut-off in the manner shown). If the applied seriesof impulses be positiva tube T1' with switch I6 set as shown will pass on these impulses in the -same polarity to the grid of tube 3 T2 so as to make the latter conduct for each applied impulse. It is clear that each time tube T2 is for an instant thus rendered conductive,

,the voltage across condensers i8 and I9 is very throwing switch I to its alternate position, and

positive impulses could again have been applied to the grid of saw-tooth converter tube T2. Thus,

the form shown is equally adaptable to ,applied impulses of either polarity sense;

As noted, each time condensers I8 and IS` are,v

discharged by the momentary conductivity of tube T2, such discharge is to the same voltage level. Since the point between eondensers I8 and I9 is fixed with a iixed impedanceeither side of it, the voltage at this point will drop to a xed level (assuming the average periodicity of applied impulses to be substantially constant) Yfor each discharge of condensers I8 and I9 as aforesaid,A and will always vary proportionally with voltage variations across both condensers I8 and IS in series. In order not noticeably to affect the ability of point 2B to assume the same potential with each discharge of condensers I8 and I9, Vand in order to be able to use the potential across condenser I9 for further operation of the circuit, I prefer to make a relatively high impedance connection thereto as a coupling .to clipper Il. shown, this connection comprises a di rect link to the Vgrid of clipper tube T3 and a high'. resistance bias resistor ZI -or biasing tube T3 preferably below cut-ofi. For reasons that will laterbecome apparent, tube T3 is Selected to have a relatively steep characteristic so that it will saturate ata point corresponding to a, relatively small grid voltage increase above that required to 4'produce cut-off conditions. In this manner, tube T3v performs both a clipping and limiting action; and by adjusting the slope of the characteristic of this tube, as mentioned, while making the saw-tooth signals applied thereto very strong, it is possible to produce in the output thereof a signal which shifts between one substanti'ally constant magnitude and another substantially constant magnitude during the short periods in which tube Ta is operated on the steep portion of its characteristic.

As above indicated, it is possible by ldiiierentiating the output of clipper tube T3 to generate an impulse for each of these short shifts. Accordingly, a differentiating network having a suitable time-constant, as afforded by condenser 22 shunted to ground by a resistor 23, is directly connected across the output of tube T3. The differentiator network thus supplies impulses of onepolarity sense for each traversal of grid voltage across the characteristic of tube Ts in the increasing direction, and impulses of opposite polarity for each traversal in the decreasing grid voltage direction. As further noted above, one of these sets of impulses (i .e. in one polarity sense) is delayed as desired with respect to applied impulses, and the other set is not indicative of delay. Inasmuch as these latter impulses do not indicate delayed energy, they are not desirable and may be eliminated by a clipper device which in the form shown comprises a pentode T4. As shown, pentode T4 is provided with two alternate output means 24, 25 depending upon what polarity is desired in the delayed impulses. Thus output connection 24 is taken from the anode circuit of tube T4, and output connection 25 is taken from the cathode circuit thereof.

AY clear understanding `of the apparatus thus far described may be had by reference vto some of the voltage curves shown in Fig. 4. In this lligure, curve a represents an irregular series of applied impulses (as supplied, for example, by a time-modulation system in accordance with the teachings of the above-mentioned application Serial No. 386,282 `or E, Labin), and curve b showsthe'type of saw-tooth wave produced 'by tube T2 in response to each impulse of the series shown in curve a'. It will be noted that the sloping portion 0i each saw-tooth in curve b is shown as being the same and substantially linear throughout. This condition is deemed preferable and may be vobtained by designing elements Il', I8 and I9 appropriately so that a large timeconstant with respect to the contemplated average recurrent periodicity of impulses is thereby dened.v

The action of clipper II is further shown on curve b with the dotted lines 26 and 21. Line 26 may represent the voltage level below which clipping action in tube T3 takes place, and line 2l may represent the voltage level above which the limiting action explained above occurs. Thus it will be seen that the output of clipping device II may alternate vbetween two substantially uniform voltages proportional to the levels 26 and 2l and shift from one to the other of these voltages each time a saw-tooth wave traverses limits of the voltage region between levels `26 and 21, as will be clear. Since each time the saw-tooth wave crosses the voltage region between limits 26 and 2l, and there is thus a change in voltage output of tube T3, there will be generated in the output of diierentiator I2 an impulse of one polarity, say impulse 28 (curve lc) for each traversal in one direction (as at 29) and an impulse 30 of opposite polarity for each traversal in the other direction (as at 31). It will be noted that all of the impulses of the polarity of impulse 28 occur in the same recurrent pattern as that of applied impulses, and that each of these impulses is delayed an amount a with respect to the applied impulse corresponding thereto, the magnitude of a depending upon the particular level of the region betweenclipper limits 26 and 2l. Thus merely by varying the bias'of the saw-tooth signal applied to tube Ts, it is possible correspondingly to vary the magnitude of the delay'. Since the series of impulses of opposite polarity (e. g. impulse 3G) corresponds with the original applied impulses,` these may be eliminated if desired by appropriate adjustment of the bias on clipper tube T4 to yield a'series of sharp and accuratelyv dlenedrdela'yed impulses, as shownV in curved. ,f y

Another preferred embodiment of the invention is illustrated by Fig. 3' which replaces some of the circuit ofA Figl 2. The circuitof Fig. 3 willV be observed to replace that of Fig. 2 from the outputo thesaw-tooth converter on; and the voltage dividing condenser arrangement I8, I9, forming part of the time-constant circuitfor the saw-tooth converter will be recognized. In this alternate embodiment a diodeclipper'32' is employed serially connecting point ZI'oi potentiometer ,ISLIl to a ilrstdiferentiating network 'comprising condenser 33 and's'hunt're sistor 34. As in the case of the clipper Ts of Fig. 2, clipper 32 is appropriately biased through a relatively high resistor 35 so that (as before) the time constant of condenser i8 and i9 and resistor 35 is sufficiently high. The effect of diode clipper 32 will thus be seen to yield a voltage output curve of the nature shown in curve e of Fig. 4, wherein all saw-tooth voltages above a certain magnitude are, limited out, depending upon the bias applied to diode 32. The subsequent effect of passage of such energy through differentiator network 33, 34 will be seen to yield a series of equal duration square waves, such as wave 36, for each applied impulse, these Waves being characterized by a short sharp impulse (e. g. 31) of opposed polarity at the leading edge thereof. As shown, the wave form of Fig. 4f is further treated by passage through a clipper amplifier T5 having its 4bias so adjusted as effectively to elimi- -nate the sharp impulses 3l characterizing the leading edges of the square waves. By taking output energy from clipper T5v in its anode circuit, a reversal in the polarity of square waves 36 may be obtained to yield a wave form as shown in Fig. 4g as will be clear. This Wave form is next applied to another differentiating circuitcomprising condenser 38 and shunt resistor 39 to produce a series of impulses of alternate polarity and of substantially the same nature shown in Fig. 4c, which will be recognized as similar to :the voltage form previously obtained with the circuit of Fig. 2 at the output of differentiating network 22, 23. It is thus clear that a. further clipper device Ts may be provided again to eliminate the undesired series of impulses 30 and to provide in outputs 4t or 4I delayed impulses of the desired polarity.

It, will be seen that I have disclosed relatively simple means for effectively delaying recurrent impulse energy, impulse for impulse. Although this delay is obtained by generating new impulses for those applied, the arrangement shown has the advantage of producing extremely sharp and Well-defined impulses at the output waves. If some passive Vnetwork had been employed to obtain the-delay, there would have been substan-` tial distortion of the original applied wave form; and it accordingly would have been increasingly diiicult to obtain Ya well-defined delayed pulse, theV larger the delay. If it be desired to produce delayed impulses of the same form as those applied to the input, the delayed impulses produced by the circuits shown Imay be used to synchronize a wave generator having suitable shaping means;

and by monitoring input pulse shapes and shaping the newly generated pulse shapes to conform thereto, the eifect of flexibly adjustable delay is produced with no apparent distortion.

Although I have disclosed the delay to be adjustably controllable, as by controlling the bias applied to the control grid of tube T3 or the bias applied to diode 32 as the case may be, it is to be understood that bias control may be effected by other means. For example, and to illustrate a practical application if it is desired that two mobile units each transmit on an impulse-modulated carrier in synchronism With each other and if these units are continuously moving with respect to each other, the abovedisclosed means may be employed to maintain such synchronism. A relatively simple expedient to effect such a result would be to employ on one of the mobile units a receiver responsive to energy transmitted by the other unit and providing a current indicative of the volume of sig- 6 nal detected. Since the volume as so detected could be proportional to the distance between the mobile units, this volume-indicative current could be employed appropriately tov control the bias on one of tubes T3 or 32 as the case may be, whereby a delayed series of impulses may be supplied for controlling impulse-modulation of energy to be transmitted from the mobile unit carrying the apparatus in accordance with the invention.

Thus, it is clear that constant synchronism could be maintained for transmission from both mobile units, no matter how their spacing with respect to each other might vary,

The apparatus in accordance with the invention is contemplated to have further use in impulse repeater units wherein impulse energy is received and detected and then re-transmitted. For more effective re-transmission it is deemed preferable that the receiver be rendered ineffective during such re-transmission, and, accordingly, some sort of delay in the received impulses after reception and up to transmission should preferably be effected. The circuitV of the invention forms a relatively simple solution to such a problem.

While I have described my invention as being particularly adaptable to the delaying of time-modulated impulse energy, it is clear that it may be equally applicable to systems employing frequency-modulated impulses-that is, impulses whose frequency of recurrence is modulated in accordance with any given signal. In such an application, however, care should be taken that the time constant of the circuit comprising resistor 2i or 35 and capacitor i9 be suiciently large so that the average periodicity of such impulses is preferably smaller vthan said time constant, as will be clear.

Although throughout the above specification and in the annexed claims reference has consistently been made to the type of energy which is fed to the apparatus as impulse energy, it is to be understood that this term embraces impulses in a broad aspect-that is, not only the relatively short abrupt form shown in the graphical representations of Fig. 4, but also any type of electrical fluctuation.

Although I have described my invention particularly in connection with the preferred forms shown, it is to be understood that many modications, additions and omissions may be made without departing from the spirit or scope thereof.

What I claim is:

1. Apparatus for effectively delaying a series of recurrent impulses a predetermined amount for each impulse thereof, comprising saw-tooth generating means including means reponsive to applied impulse energy for conditioning said generator means to deliver a saw-tooth voltage Wave for each of said impulses7 clipper means for clipping each said saw-tooth wave at a predetermined level, said clipper means comprising a thermionic tube having a, space current path, said path saturating at a constant level relatively slightly above the clipping level thereof, and differentiating means connected to the output of said clipper means.

2. Apparatus, according to claim 1, further comprising further clipping means connected to said differentiating means and including bias control means for clipping out undesired portions of the output of said differentiating means.

3. A delaying device for effectively delaying applied impulses a desired amount, comprising a source of energy supplying energy impulses, a saw-tooth generator including an electron discharge device operatively connected to said source, means for normally biasing said :discharge device below cut-off and a charging circuit inthe output of said discharge device and comprising a resistance shunted by capacity means whereby the slope of the saw-tooth wave of said generator may be determined, clipper means connected to said capacity means including means to limit said saw-tooth wave to a substantially constant level above the clippingI level, biasing means including a relatively high impedance forbiasing said clipper means, said biasing means determining said desired amount of delay of said applied impulses, and differentiating means connected to the output of said clipper means.

4. A delaying device according to claim 3, wherein said capacity means includes two condensers in series, said clipper means being connected to a point intermediate said capacity means.

5. A delaying device according to claim 3, wherein said means to limit provide a relatively steep characteristic of output current with respect to input voltage, whereby said clipper means eiectively performs both a clipping and a limiting operation on the wave form applied thereto.

6. Apparatus for effectively delaying a series of recurrent impulses a predetermined amount for each impulse thereof, comprising saw-to-oth generating means including means responsive to applied impulse energy for conditioning said generator means to deliver a saw-tooth voltage wave for each of said impulses, wave forming means including at least one wave-forming portion controlled by said saw-tooth Wave for forming a voltage wave which shifts between two values each of substantially constant magnitude intermediate the extreme values of said saw-tooth voltage, and differentiating means connected to the output of said wav-e forming means the delay for said impulses being determined by the time interval between the starting pointJ of said saw- Atooth wave and the time of operation of said one wave forming portion.

7. Apparatus according to claim 6 wherein said wave Aforming means comprises a thermionic tube having a given steepness characteristic and a control grid, the bias of said control grid determining the initiation of said Voltage shift from one of said substantially constant magnitude values 'to the other of said values, and said characteristic determiningsaid other of said values.

8. Apparatus according to claim 6 wherein the Value of one of said voltage Values is Zero.

`9. Apparatus according to claim 6 in combination with clipping means including a control means connected to said differentiating means for clipping out undesired portions of the output of said diierentiating means.

10. The method of generating a series of recurrent impulses delayed a predetermined amount with respect to a like series of impulses which comprises conditioning a first generator to initiate by each of said like impulses a sawtooth voltage wave, generating a second voltage wave which varies abruptly between lower and higher substantially constant predetermined voltage values, the lower voltage value of said Wave being determined by a predetermined value of said saw-tooth wave, the higher voltage value of said wave being determined by limiting action, and dilerentiating said second voltage wave thereby producing said series of recurrent delayed impulses.

11. The method of producing two substantially similar impulses separated by a predetermined `time interval, comprising generating a rst impulse, initiating by said iirst impulse the generation of a saw-tooth voltage wave, initiating by said saw-tooth wave when said saw-tooth Wave equals a predetermined magnitude a second voltage wave causing by limiter action voltage shifts to 'lie between said predetermined magnitude and a second predetermined magnitude, and differentiating said second voltage wave at the point of said predetermined magnitude to produce the second impulse.

DONALD D. GRIEG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 

